\documentclass{article}
\usepackage{amssymb,amsmath,amscd,concmath}
\pagestyle{empty}
\begin{document}
\begin{equation*}
v={\mathrm{d}x \over \mathrm{d}t} = \lim_{\Delta t \to 0}{\Delta x \over \Delta t}
\end{equation*}
\end{document}
